Apparatus and process for impingement cooling of a component exposed to heat in a flow power machine

ABSTRACT

Described are an apparatus and a process for impingement cooling of a component exposed to heat in a flow machine, with a wall section on which at least one impingement air flow impinges on at least one side, which passes through a flow channel within a surface element arranged spaced apart from the wall section to be cooled and which strikes against the wall section to be cooled.  
     The invention is distinguished in that the flow channel has an inlet aperture and an outlet aperture, that the outlet aperture directly faces toward the wall section to be cooled, and that the inlet aperture has a throughflow cross section which is smaller than the throughflow cross section of the outlet aperture.

FIELD OF THE INVENTION

[0001] The invention relates to an apparatus for impingement cooling of a component exposed to heat in a flow machine with a wall section to be cooled which is acted on, on at least one side, by at least one impingement cooling air stream, which passes through a flow channel within a surface element spaced apart from the wall section to be cooled and strikes the wall section to be cooled. Furthermore the invention relates to a cooling process related to this and to a process for the production of a heat resistant component.

DESCRIPTION OF PRIOR ART

[0002] The maximum output power attainable with modem gas turbine plants, and also the efficiency attainable with these plants, depend directly on the combustion temperatures attainable within the combustor, and at which the resulting hot gases flow through the turbine stages provided downstream. From purely thermodynamic viewpoints, the efficiency of such flow power machines could be definitely raised by an increase of the combustion temperatures attainable within the combustor, but limits are set on this endeavor by the materials of those components which are directly or indirectly impinged on by the hot gases. Thus from viewpoints purely specific to the materials, care has to be taken to keep the temperatures prevailing within gas turbines below the melting temperatures of the respective components concerned. In order nevertheless to be able to attain the highest possible combustion temperatures, on the one hand new, high temperature resistant materials are always being developed, and on the other hand cooling measures are found in order to cool those components directly exposed to the hot gases, so that the thermal stress is reduced and the life of the components is increased.

[0003] From the many components to be cooked within a gas turbine plant, it is precisely the guide and rotor blades within a turbine stage directly following the combustor which are not only exposed to the hot gases, but also have to withstand high mechanical loads.

[0004] Usually cooling air is specifically applied to just such components; it is branched off in partial flows from sides of the compressor and conducted directly to the components to be cooled through correspondingly provided cooling channels. In particular, it is effective to cool those regions of the turbine blade which are exposed to a particularly heavy thermal stress. This primarily concerns the turbine blade front edge, upon which the hot gases strike directly, bringing about particularly high heat transfer numbers in this region. The maximum of the so-called external heat transfer coefficient is typically reached at those places of the turbine blade front edge upon which the hot gases strike perpendicularly and thus lead to a maximum ram action on the turbine blade front edge. To cool with maximum efficiency at just these places is essential in order not to exceed the temperature limits that depend on the materials.

[0005] A preferred technique for cooling the turbine blade front edge is based on the specific cooling air supply within the turbine blade along the cooling channels situated within the blade, the cooling air being conducted past, directly on the inside of the turbine blade front edge in order to cool the front edge convectively.

[0006] A turbine blade constituted in this manner can be gathered, for example, from U.S. Pat. No. 5,603,606, in which according to FIG. 1 in this document a cross section is shown through the forward region of a turbine blade, which has a cooling air channel 166 which is connected via a connecting gap 180 to a forward cooling volume 168 that directly borders on the interior of the turbine blade at the turbine blade front edge. The connecting channel 180 is bounded on one side by the turbine blade inner wall, so that the cooling air conducted into the forward volume region flows tangentially over the inside of the turbine blade front edge. The whole region of the turbine blade front edge is hereby acted on by an internal cooling air flow; however, this is able to cool only insufficiently just the abovementioned hot regions along the turbine blade front edge.

[0007] In order to improve the contact, and the related heat exchange, between the cooling air flow, it was proposed in DE 32 481 62 C2 to install rib elements on the wall surface to be cooled, with their rib long axes oriented at about 45° to the direction of the cooling air flow. The heat transfer between the cooling air flow and the surface to be cooled can admittedly be improved by the measure described above; however, the cooling air flows only tangentially of the surface to be cooled, so that particularly hot regions of the wall surface are likewise not cooled to a sufficient extent.

[0008] In order to eliminate this disadvantage, a cross section through the front region of a turbine blade 1 is shown in FIG. 4. To clarify the heating problem, flow lines 2 are schematically drawn in, which are to represent the hot gases striking the turbine blade front edge 3. In particular in that region of the turbine blade front edge 3 at which the hot gas flow 2 strikes nearly perpendicularly on the turbine blade front edge, an extremely strong temperature rise takes place within the material of the turbine blade. It is just this region which has to be cooled particularly effectively. For this purpose, an internal cooling channel 4 is provided for the turbine blade 1, and is connected with a forward volume 6 by means of at least one connecting channel 5 [sic], which is situated in a partition 8, and into which there likewise projects an outlet channel 7 connected to the upper side of the turbine blade.

[0009] Cooling air which is supplied at high pressure via the cooling channel 4 enters at high speed into the volume 6 through the flow channel 5 and strikes the region 3 of the turbine blade front edge. This cooling technique, known as impingement cooling, in contrast to the abovementioned cooling techniques, is able to strongly cool that region on the turbine blade front edge which is most heavily thermally stressed by the hot gases. More exact investigations of the impingement air flow, known per se, passing through the connecting channel toward the turbine blade front edge to be cooled show however that the flow channel, constituted straight, only permits a widening out of the cooling flow on leaving the connecting channel. Only small surfaces on the inside of the turbine blade front edge are hereby effectively acted on by cooling air, and the cooling effect is restricted to only a greatly limited region. A further disadvantage of the straight constitution of the cooling channel is that the emerging cooling flow very heavily cools a very small region and therefore contributes to very high temperature gradients and the resulting stress gradients in the material.

SUMMARY OF THE INVENTION

[0010] The invention has as its object to further develop an apparatus for the impingement cooling of a component exposed to heat in a flow machine, preferably a turbine blade, according to the abovementioned category, so that the region of the heat-stressed turbine blade front edge is cooled as effectively and optimally as possible, so that account can be correspondingly taken of the endeavor to reach higher combustor temperatures or a reduction of the cooling requirement.

[0011] A process for the production of such a component is also given.

[0012] The object of the invention is attained by means given in claim 1. The subject of claim 12 is a process according to the invention for impingement cooling. Claim 14 relates to a production process according to the invention of a component according to claim 1. Advantageous features developing the concept of the invention are the subject of the dependent claims and also will be apparent from the whole specification, with particular reference to the embodiment examples according to the drawings.

[0013] According to the invention, the apparatus for impingement cooling of a component exposed to heat in a flow machine, with a wall section exposed on at least one side to an impingement cooling flow which passes through a flow channel within a surface element spaced apart with respect to the wall section to be cooled and strikes against the wall section to be cooled, is constituted such that the flow channel has an inlet aperture and an outlet aperture, that the outlet aperture directly faces the wall section to be cooled, and that the inlet aperture has a flow cross section which is smaller than the flow cross section of the outlet opening.

[0014] The idea on which the invention is based, in contrast to the prior art, has the flow channel embodied such that the cooling flow passing through the flow channel is strongly fanned out divergently, and in this manner covers a greater region of the turbine blade front edge to be cooled. If the contour of the flow channel is formed according to the invention with a flow cross section widening out in the flow direction, the pressure losses are moreover reduced, which again is of benefit to the cooling action of the cooling air stream passing through the flow channel, especially as the impingement air cooling flow through the flow channel is slowed down. This is likewise the reason why the flow losses which arise directly at the outlet opening of conventionally constituted flow channels can be considerably reduced.

[0015] By the measures according to the invention, not only can the cooling action be considerably improved in the region of the turbine blade front edge, but also the impingement air cooling flow, striking divergently on the inner side of the turbine blade front edge, contributes to a better equalization of the temperature gradient which is formed within the turbine blade front edge. This also likewise reduces the mechanical stresses arising within the turbine blade, so that, not least, a definite contribution to the reduction of material fatigue is provided. Summarizing, it can be established that the measure according to the invention contributes to a homogenizing of the heat transfer numbers occurring along the turbine blade surface due to the internal cooling. Overheated places along the turbine blade front edge, over which the ram pressure of the hot gases has a maximum, can be effectively avoided.

BRIEF DESCRIPTION OF THE DRAWING

[0016] The invention is described hereinafter by means of examples, without limitation of the general concept of the invention, using embodiment examples with reference to the accompanying drawing.

[0017]FIG. 1 is a cross sectional view through the forward portion of a turbine blade with impingement air cooling constituted according to the invention,

[0018]FIG. 2 is a detail view of a flow channel constituted according to the invention,

[0019]FIG. 3 is a schematized longitudinal sectional view through a turbine blade, and

[0020]FIG. 4 is a cross sectional view through the forward portion of a turbine blade according to the state of the art.

PREFERRED EMBODIMENTS OF THE INVENTION INDUSTRIAL USABILITY

[0021]FIG. 1 shows the forward region of a turbine blade 1 in a cross sectional view, with a main cooling channel 4, which is connected via a flow channel 5 to a forward cooling volume 6, which besides is separated from the main cooling channel 4 by a partition 8. The forward cooling volume 6 has an outlet channel 7 which opens at the surface of the turbine blade 1. The cooling air supplied through the main cooling channel 4 passes at high pressure through the flow channel 5 and strikes against the inner wall of the turbine blade 1 situated opposite the flow channel 5 in the region of the turbine blade front edge 3. According to the invention, the flow channel 5 is constituted with a flow cross section which widens out in the flow direction, so that the cooling air passing through the flow channel 5 in the form of an impingement air cooling stream emerges divergently from the flow channel 5 and thus impinges on a greater region of the turbine blade front edge 3.

[0022]FIG. 2 shows a detail diagram relating to the geometrical constitution of the flow channel 5 which is provided within the partition 8 which separates the main cooling channel 4 from the forward volume 6. The flow channel has an inlet aperture 9 and also an outlet aperture 10, the inlet aperture 9 having a smaller cross section, or a smaller aperture diameter, than the outlet aperture 10. In the embodiment example shown, the flow channel 5 is constituted conically widening and has bounding walls cut in a straight line. It is however also basically possible to provide funnel-shaped, curved bounding wall contours. It is fundamental that the impingement air cooling flow propagating along the flow channel 5 widens out divergently in flow profile after passage through the flow channel, in order in this manner to impinge on as large as possible a region of the turbine blade front edge 3, as impingement air cooling.

[0023] Typically, the aperture angle shown in FIG. 2 and included between the mid-axis through the flow channel 5 and a bounding wall has values between 2° and 9°. Typical average diameters for the flow channel 5 are in the range between 0.5 and 7 mm.

[0024] A longitudinal section through the forward region of a turbine blade 1 is shown in FIG. 3, with the main cooling channel 4, the front volume 6, and also the partition 8, in which numerous individual flow channels 5 are distributed radially of the turbine blade 1. All the individual flow channels 5 are oriented relative to the turbine blade front edge 3 so that the individual impingement air streams passing through the flow channels are able to directly cool the inner wall of the turbine blade front edge.

[0025] For the production of the turbine blade constituted according to the invention, the conventional casting process is suitable, in which, within a casting mold for forming the flow channels constituted according to the invention, heat resistant insert shapes are provided which are subsequently removed from the casting in order to lay open the free flow channels.

[0026] For FIG. 4, reference is made to the implementations described at the beginning. List of Reference Numerals  1 turbine blade  2 hot gas flow  3 region of the turbine blade front edge  4 cooling channel, main cooling channel  5 flow channel  6 forward volume  7 outlet channel  8 partition  9 inlet opening 10 outlet opening 

1. Apparatus for impingement cooling of a component (1) exposed to heat in a flow machine, with a wall section (3) exposed on at least one side to at least one impingement air cooling flow which passes through a flow channel (5) within a surface element (8) spaced apart with respect to the wall section (3) to be cooled and strikes against the wall section (3) to be cooled, wherein the flow channel (5) has an inlet aperture (9) and an outlet aperture (10), the outlet aperture (10) directly faces the wall section (3) to be cooled, and the inlet aperture (9) has a flow cross section which is smaller than the flow cross section of the outlet opening (10).
 2. Apparatus according to claim 1, wherein the flow channel (5) has a cross section which monotonically widens out in the flow direction.
 3. Apparatus according to claim 1 or 2, wherein, in longitudinal section through the flow channel (5), a line joining a point of the inlet opening (9) to a point of the outlet opening (10), both points being situated in the same half plane of the longitudinal section, includes with the flow channel long axis an angle of 2° through 9°.
 4. Apparatus according to one of claims 1-3, wherein the flow machine is a gas turbine, and the component exposed to heat is a turbine blade (1), whose wall section to be cooled is the turbine blade front edge (3).
 5. Apparatus according to claim 4, wherein at least one cooling channel (4) is provided extending radially of the turbine blade (1) and is bounded by a partition (8) in the direction of the turbine blade front edge; the partition (8) encloses a volume (6) with the turbine blade wall in the region of the turbine blade front edge (3); and the partition (8) is the surface element with at least one flow channel (5), and the turbine blade wall facing toward the partition is the wall section to be cooled.
 6. Apparatus according to claim 5, wherein the flow channel (5) includes a channel longitudinal axis which intersects the turbine blade wall at the inside of the turbine blade front edge (3).
 7. Apparatus according to claim 6, wherein the channel longitudinal axis intersects the turbine blade wall orthogonally at the inside of the turbine blade front edge (3).
 8. Apparatus according to one of claims 5-7, wherein numerous flow channels (5) are arranged in a radial direction within the partition (8).
 9. Apparatus according to one of claims 5-8, wherein at least one flow channel (7) out of the volume (6) enclosed by the partition and the turbine blade wall is provided.
 10. Apparatus according to claim 9, wherein the outflow channel (7) projects through the turbine blade wall.
 11. Apparatus according to one of claims 1-10, wherein the inlet aperture (9) has an aperture diameter of at least 0.5 mm.
 12. Process for cooling a component (1) exposed to heat with a wall section (3) to be cooled by means of impingement cooling, in which the wall section (3) to be cooled is impinged on at least one side with an impingement air cooling flow, wherein the impingement air cooling flow is directed with a divergent flow profile onto the wall section (3) to be cooled.
 13. Process according to claim 12, wherein cooling air is conducted through a flow channel (5) with a flow cross section running divergently in the flow direction and, downstream of the flow channel, directly strikes against the wall section (3) to be cooled.
 14. Process for the production of a component (1) exposed to heat in a flow machine, with a wall section (3), to be cooled by means of impingement cooling, exposed on at least one side to at least one impingement air cooling flow which passes through a flow channel (5) within a surface element (8) arranged spaced apart with respect to the wall section (3) to be cooled and is arranged on the wall section (3) to be cooled, passes through and strikes against the wall surface (3) to be cooled, wherein the component (1) exposed to heat is produced by means of a casting mold in a casting process; and the casting mold provides an insert shape at the place of the flow channel (5), to be subsequently removed from the casting.
 15. Process according to claim 14, wherein the insert shape consists of a kind of conically shaped cork, which is separated from the casting so that the flow channel (5) is formed. 